Autosomal mutation in man that produces deficient activity of galactokinase (GK) or galactose-1-p uridyltransferase (GT) are being 0tudied by population, cell culture and molecular approaches. The objectives are: 1. To estimate the frequency of mutant genes in the population which produce a deficiency of either galactokinase or gal-1-P uridyltransferase and assess what clinical effects these mutations may have on growth and development. 2. To explain the occurrence of significantly lower red cell galactokinase activity found in blacks as compared to whites. 3. To relate the molecular defect in transferase deficiency galactosemia to catalytic malfunction and determine whether there is genetic heterogeneity among different galactosemic patients. 4. To study the molecular and biochemical effects of galactose enzyme deficiencies in human diploid cell cultures, and use interspecific somatic cell hybrids to localize the galactose enzyme to specific loci on human chromosomes.